Hydrofluoric Acid Corrosion Testing on Unplated and Electroless Gold-Plated Samples

The Molten Salt Reactor Experiment (MSRE) remediation requires that almost 40 kg of uranium hexafluoride (UF{sub 6}) be converted to uranium oxide (U{sub 3}O{sub 8}). In the process of this conversion, six moles of hydrofluoric acid (HF) are produced for each mole of UF{sub 6} converted. The entire conversion process can be summarized by the following reaction: UF{sub 6} + 3H{sub 2}O {yields} UO{sub 3} + 6HF. (The UO{sub 3} is not stable at high temperatures and therefore decomposes to U{sub 3}O{sub 8}). HF is well known for its ability to attack most metals and silica-containing compounds. It reacts rapidly to destroy protective films and can be fatal in very small quantities (e.g., 2% exposure of the body or 50 ppm in air). Because most of the conversion system is made of various metals, the sections that come in contact with HF must be able to withstand corrosion, high temperatures, elevated pressures, and radiation. Consequently, most of these sections will be plated with gold for increased protection of the metal. This report summarizes the results from the tests that were performed on the metal samples. Section 2 covers the approach to the tests, gives a general background of the sample preparation, and then reports the data from the tests. The final section presents a discussion of what was learned from the data and recommendations for uses of these metals in the MSRE conversion process